Your processor must support VT and also have it enabled for you to be able to use Hyper-V in Windows 2008 server 64bit.
To do this on a Dell 2950, follow the steps below.
Go into the BIOS by pressing F2 as the server is booting.
Use the down arrow key to go down to CPU Information and press enter.
Use the down arrows to go down to Virtualization Technology and press the space bar to enable it.
Press Escape twice , then choose Save changes and Exit.
The server will do a hard power down by itself, then reboot.
Once Windows has booted, you can then check to make sure that Hyper-V is running and has no errors in the event log for it.